Green’s Dictionary of Slang

(UK tramp) a tramp’s mark, used to inform fellow vagrants .

1929

Advertiser (Adelaide) 25 Oct. 32/8: No ‘maunderer’ (tramp) nor ‘fencer’ (door to door hawker) need ‘clem’, (starve), or do without ‘chow chow’ (food) if he follows the many ‘patterans’ (private marks) which tramps make on or near the doors of generous householders.